The invention relates to a ship propulsion system with a synchronous machine which includes    a) a rotor with a multi-pole rotor winding to be cooled to low temperatures, in particular to superconducting temperatures, wherein the rotor winding is thermally coupled directly or indirectly to a rotor cooling system, and    b) a stator surrounding the rotor with            a cooled, normal-conducting stator winding,        a support structure which at least partially supports the stator winding, the support structure having an essentially hollow-cylindrical outer body made of a soft-magnetic material and axially and radially extending fin-shaped support teeth disposed on the inside of the support structure, with at least sections of the stator winding being arranged between the support teeth,        an outside housing with a hollow-cylindrical housing section surrounding the outer body, and        a stator cooling system for dissipating heat generated by the stator winding to water as cooling medium.        
A corresponding ship propulsion system with a synchronous machine is disclosed in WO 03/019759 A2.
The synchronous machine of the conventional ship propulsion system includes a rotor with a multi-pole rotor winding formed of conductors made of a high-Tc-superconducting material. The winding is housed in a vacuum-insulated cryostat adapted to receive a cryogenic cooling medium and must be maintained at an operating temperature between 15 K and 77 K. The stator winding of the machine is formed as a so-called air gap winding arranged to between non-magnetic support teeth. Cooling channels extending radially, axially, and/or in the circumferential direction are provided to effectively cool the winding sections, with water as cooling medium flowing through the channels. The radial dimensions of the support teeth are relatively large for accommodating the channels and for providing a sufficiently large cross-section for the cooling medium, so that the stator winding of the conventional machine can be sufficiently and effectively cooled.
However, the radial dimension is limited in some types of machines. In those types of machines having a relatively small outside diameter, heat generated in the stator winding is difficult to dissipate using such stator cooling system and a liquid cooling medium. These types of machines are required, in particular, for propeller and jet propulsion systems in floating units, such as ships.
Advantageous oceangoing capabilities of a marine surface ship are characterized by high speed and excellent maneuverability. A high continuous speed is required to provide good mobility over large distances. High top speeds and mobility are also required, although sometimes only for short durations. The continuous speed is around 20 knots, and the top speed should be in excess of 30 knots.
One important property is the operational endurance at sea, which depends on the supply of fuel, water and provisions as well as the operational reliability of the systems and the readiness of the crew. Today, high continuous speeds in rough seas in conjunction with excellent maneuverability have become a prerequisite for covering large distances. The ships must be ready for action worldwide.
For improved oceangoing properties, the systems and components of the propulsion and onboard networks must have a high functional availability. They must be structured so that damage to the components and their networking, for whatever reason, is identified by suitable sensors and damaged systems are disconnected from the propulsion and onboard network, so that the unaffected network can continue to operate with as little interruption as possible.
Several aspects for designing a propulsion system for a ship will now be discussed:
I. Propeller Propulsion System
Surface ships are typically driven by screw propellers. Diesel engines or gas turbines are arranged in the inside the ship, which transfer the mechanical energy to the propellers by way of shaft systems/gears. Based on recent operating experiences, marine propulsion systems have to meet particularly severe requirements, namely                rapid startup capability,        high maximum power with overload for short times,        a small weight,        excellent maintenance capabilities, as well as good installation and removal paths,        low fuel consumption,        high operational reliability.        
The diesel engine has proven an ideal propulsion system for smaller marine vessels due to its relatively rapid startup capability, its construction and operating characteristic which saves space and personnel, and its low specific fuel consumption.
II. Water Jet Propulsion System
Such propulsion systems are used, in particular, in fast oceangoing ships and include a drive having at least one water jet, which is generated by a pumping system with an exit nozzle or nozzles. An impeller can be provided on one end of a pump shaft which is connected to a motor, such as an electric motor with, for example, high-Tc-superconductors, or to a diesel engine or a gas turbine (see, for example, also WO 03/101820 A1).
III. Fully Electric Ship (FES)
The electric onboard network of modern ships is composed of the following components and systems, namely                electric energy generation,        electric energy distribution, and        electric energy consumers.        
Since several years, the feasibility of fully electric marine surface ships has been investigated. The fully electric ship (FES) employs economical electric energy generators for propelling the ship with electric machines (propulsion network) and for supplying power to the onboard network.
Small experimental platforms are in operation since several years or are presently under construction. The electric propulsion and onboard networks mostly employ low voltages.
The following future technologies may be useful for generating electric energy:                fuel cell technology        gas turbine-generator-segments        diesel engine-generator-segments.        
The power requirements of systems generating electric energy for future ships are in the range of 20-50 MW depending on the demand from the onboard network and the speed of the vessel. Only an intermediate voltage system will be practical for distributing electric power at these power levels. DC distribution networks are also contemplated, because the fuel cell technology inherently produces a DC voltage.
The voltages used in onboard networks of future marine surface ships are in the low voltage and intermediate voltage range. The frequency of the onboard network is 60 Hz (sometimes 50 Hz).
Propulsion systems are contemplated, in particular in the context of the development of fully electric ships, which have at least one electric propulsion engine that is attached in the form of a pod to the underside of the ship's hull. Such propulsion systems are also referred to as “POD propulsion systems.” Propulsion systems of this type, in particular with synchronous machines employing high-Tc-superconductors, are generally known (see, for example, WO 03/019759 A2, EP 0 907 556 B1, WO 03/047962 A2).
The most important objective in the design of these POD propulsion systems is a reduction of their weight.
Another objective is to achieve a hydrodynamic propeller efficiency of greater than 60%. The ratio POD diameter/propeller diameter is an important criterion for the POD propulsion system and should optimally be around 0.3 . . . 0.33 (ratios lower than 0.3 produce only very small hydrodynamic advantages at the expense of an extraordinary high complexity for the POD).
The nacelle should have a relatively short length.
Conventional permanent magnet machines, conventional asynchronous and synchronous machines do not meet the requirements of aspect ratio and weight.